You can do a fresh install, or a dirty install, similar to when one installs windows on top of itself. It's your choice. Just make sure if you install it on top of itself, you backup your home profile to a FAT32 partition (avoids permission and owner problems later), then allow the dirty install to overwrite all files, make sure you use same user name on install, then be careful of what you add back into the profile folder. I would advise only adding one thing at a time in case something there cause the problem. That way if things go badly again when one is added back, you know where the problem was. Most would advise a clean install however from a known good ISO, an ISO that passed the sha256sum check.